This invention pertains to an improved combustion chamber for a condensing furnace, and more particularly to a novel combustion chamber for a condensing furnace in which an air-fuel mixture is burned relatively silently and in an efficient manner.
Condensing heating apparatus or pulsating combustion heating apparatus has been described in the prior art. See, for example, Hallowell U.S. Pat. No. 4,164,210 and Kitchen U.S. Pat. Nos. 2,916,032, 3,267,985, 4,241,723, and 4,309,977. However, none of the described devices have been made and sold on a commercial basis for residential or commercial heating. The present invention stems from the Hallowell device as disclosed in U.S. Pat. No. 4,164,210, and is embodied in the first successful commercially available condensing gas furnace, which is made by Lennox Industries Inc. and presently identified as the G14 series. Basically in the disclosed Hallowell device, a combustible fuel gas and combustion air are admitted into a combustion chamber. To start the combustion cycle, a spark plug is used to ignite the fuel gas-air mixture to produce an internal explosion, with resultant generation of heat. Immediately after each such explosion, an accoustically-produced negative pressure in the combustion chamber draws additional air and fuel gas into the combustion chamber through appropriate air and gas valves, whereupon the next explosion occurs and closes the valves until the next negative pressure occurs. Once started, a series of heat releasing explosions are produced with combustion air and fuel gas being drawn into the combustion chamber intermittently through appropriate air and gas inlet valves. In response to the combustion chamber pulses of high pressure, the hot exhaust gases from the combustion chamber are normally expelled forcefully through an exhaust pipe to an exhaust expansion chamber from which an exhaust pipeline extends.
Room air to be heated may be passed by forced draft over the combustion system and then returned in heated condition to the room. Additional transfer of heat to the room air is obtained by providing a heat exchange coil with fins on the exhaust pipeline. Such heat exchange coil recovers and transfers to the room air the latent heat of vaporazation of the gas passing through the heat exchanger coil. A flue gas outlet is connected to the heat exchange coil for discharge of flue gas to the exterior. A drain line for condensing water is connected to the heat exchanger coil.
The prior art recognized that internal explosions within the combustion chamber caused loud noise. Various forms of combustion chambers and of muffler arrangements for such combustion chambers were proposed to attenuate the loud noise. Such loud noise would be particularly objectionable if the heating device or furnace was to be adapted for residential heating use. Consideration was also given in the prior art to encasing the combustion chamber and/or the condensing furnace cabinet in sound insulating material that would assist in the absorption of the sound and vibration caused by the pulsating combustion process. For example, Kitchen U.S. Pat. No. 4,309,977 suggests supporting the combustion chamber of a pulsating combustion apparatus in a concrete casing. Kitchen U.S. Pat. No. 3,267,985 suggests placing sound insulation in the space between the outer casing and the inner casing of the pulsating combustion furnace.
The combustion chamber of Hallowell U.S. Pat. No. 4,164,210 is a tube, which would be relatively noisy in operation. Kitchen U.S. Pat. No. 4,241,723 reveals a combustion chamber comprised of a pot-shaped bronze casting. The combustion chamber of Kitchen U.S. Pat. No. 4,309,977 is comprised of two iron castings secured together by bolts. The combustion chambers of Kitchen U.S. Pat. Nos. 4,241,723 and 4,309,977 are incapable of functioning as efficiently as that of the present invention. None of these prior art references teaches or suggests the novel combustion chamber of this invention which not only is relatively quiet, but also burns the air and fuel gas efficiently so as to increase performance in a practical and commercially feasible condensing furnace.
An object of the present invention is to provide a condensing furnace with an improved combustion chamber wherein disadvantages and deficiencies in prior constructions are obviated.
Another object of the present invention is to provide an improved combustion chamber for a condensing furnace made from a cast metal body having a fuel inlet and a port for receiving means for igniting the air-fuel mixture, said fuel inlet and said port being diametrically opposed to one another to enhance the ignition of the fuel and air.
Yet another object of the present invention is to provide an improved combustion chamber for a condensing furnace, such combustion chambers comprising an elongated cast body defining a mixing chamber and an expansion chamber, with the ratio of the transverse cross sectional area of the expansion chamber to the transverse cross sectional area of the mixing chamber being in the range of about 2/1 to 2.4/1 to maintain continuity of the pulse combustion operation.
A further object of the present invention is to provide a condensing furnace with an improved combustion chamber, wherein the ratio of the maximum Btu input for the condensing furnace with respect to the volume of the mixing chamber of the combustion chamber is in the range of 4,500/1 to 4,800/1.
Other objects and advantages of the present invention will be made more apparent hereinafter.